Glass substrate for a magnetic disk with roughened edges

Abstract

A glass substrate for a magnetic disk having an inner peripheral edge and an outer peripheral edge, wherein the surface of at least the inner peripheral edge is treated by etching to have a surface roughness such that, as measured by a three dimensional scanning electron microscope at randomly selected at least four places with a reference length of 240 μm and a cut-off wavelength of arithmetic mean roughness (Ra) of 80 μm, the mean value of arithmetic mean roughness (Ra) is from 1.0 to 6.0 μm, and the mean value of the number of peaks is within a range of from 8 to 30.

What is claimed is: 
     
       1. A glass substrate for a magnetic disk having an inner peripheral edge and an outer peripheral edge, wherein the surface of at least the inner peripheral edge is treated by etching to have a surface roughness such that, as measured by a three dimensional scanning electron microscope at randomly selected at least four places with a reference length of 240 μm and a cut-off wavelength of arithmetic mean roughness (Ra) of 80 μm, the mean value of arithmetic mean roughness (Ra) is from 1.0 to 6.0 μm, and the mean value of the number of peaks is within a range of from 8 to 30. 
     
     
       2. The glass substrate for a magnetic disk according to claim 1, wherein the surface roughness of the surfaces of both the inner and outer peripheral edges is within the range as defined in claim 1. 
     
     
       3. The glass substrate for a magnetic disk according to claim 1, wherein the surface of at least the inner peripheral edge is treated by chemical reinforcing treatment. 
     
     
       4. A magnetic disk having a magnetic recording layer formed on the glass substrate for a magnetic disk, as defined in claim 1.